Every day at 11 a.m., a few big banks tell the British Bankers' Association what it costs them to borrow. Out of that comes LIBOR — the London Interbank Offered Rate, a dull but vital interest rate that underpins trillions of dollars of transactions globally, from home mortgages and personal credit cards to major corporate lending.

Now it turns out that at least some of those same banks may have been trying to manipulate the numbers to gain a small edge in the market — an edge that might win them a few tens of thousands of dollars, while driving up borrowing costs by billions for consumers and businesses around the world.

Marcus Agius, the chairman of British banking giant Barclays, announced his resignation Monday over the scandal, and the bank paid a $453 million fine. Barclays emails show traders agreeing to manipulate the numbers they reported almost casually. The United Kingdom is launching an investigation, and regulators elsewhere in Europe and in the United States have inquiries of their own into Barclays and other big banks.

Planet Money's Adam Davidson talked with Robert Siegel on All Things Considered, exploring what LIBOR is, why it's so important, and how the allegations of manipulation may have cost consumers and businesses billions.

One point Davidson made: Emails show Barclays bankers appeared willing to impose big additional costs on the world's borrowers in an effort to get relatively small gains for their company.

"It's just shocking to read the casual, offhanded way they talk about lying to the British Bankers' Association so that they could make thousands of dollars in profit," Davidson says. "But the impact could be billions of dollars around the world. If you change this core fundamental rate it's conceivable that nearly every loan in the world is a bit more expensive than it should be."

Barclays' ability to manipulate LIBOR significantly on its own might be limited by safeguards in the way the rate is calculated. But regulatory inquiries into other big banks suggest cheating may have been more widespread.

"What we know is well over a dozen other banks are being investigated by U.S. and U.K. authorities," Davidson says. "And if it turns out that this number has been the product of a coordinated — or even an uncoordinated — series of self-serving lies by over a dozen banks, then it really calls into question the entire way that our global financial architecture works."

Imagine you could call up a friend and say, "Meet me at the bar and tell me what's going on with the economy." Now imagine that's actually a fun evening. That's what we're going for at Planet Money. Want to know more? Check out our "about" page. Want to connect with the Planet Money team? Send us an email.